Oil or gas is obtained from a subterranean formation by drilling a wellbore that penetrates a hydrocarbon-bearing formation. It is desirable to maximize both the rate of flow and the overall amount of flow of hydrocarbon from the subterranean formation to the surface.
Wellbores often penetrate subterranean formations that contain unconsolidated particulates that may migrate when oil, gas, water, or other fluids are produced or flowed back from the subterranean formation.
One way that the rate of hydrocarbon flow and the overall amount of hydrocarbon flow can be reduced is by fines production or sand migration in the formation or by precipitation. The relatively high velocity in the permeable matrix of the subterranean formation near the wellbore is sometimes sufficient to mobilize particulates. These particulates can be carried and then plug flow channels in the formation, a proppant pack, or a gravel pack. It is desirable to minimize fines or sand migration, since such particulates block flow paths, choking the potential production of the well. In addition, such particulates can damage downhole and surface equipment, such as screens, pumps, flow lines, storage facilities, etc.
Devices such as screens and slotted liners are often used to provide support for these unconsolidated formations to inhibit formation collapse. Usually, the annulus around the support device is gravel packed to reduce the presence of voids between the device and the borehole. Typically, such gravel packing operations involve the pumping and placement of a quantity of a desired size of particulate material into the annulus between the tubular device and the borehole of the wellbore. Gravel packing forms a filtration bed near the well bore that acts as a physical barrier to the transport of unconsolidated formation fines with the production of hydrocarbons. These support devices provide support for the wellbore and gravel packing and prevent some fines from entering the hydrocarbon flow into the well.
A common type of gravel packing operation involves placing a gravel pack screen in the well bore and packing the surrounding annulus between the screen and the well bore with gravel of a specific mesh size designed to prevent the passage of formation sand or fines. The gravel pack screen is generally a filter assembly used to retain the gravel placed during gravel pack operation. A wide range of sizes and screen configurations are available to suit the characteristics of the gravel pack sand. Similarly, a wide range of gravel sizes is available to suit the characteristics of the unconsolidated or poorly consolidated particulates in the subterranean formation. The resulting structure presents a barrier to migrating sand from the formation while still permitting fluid flow.
Gravel packs can be time consuming and expensive to install. Due to the time and expense needed, it is sometimes desirable to place a screen without the gravel and, particularly in cases in which an expandable screen is being placed, it may be unrealistic to place a bed of gravel between the expandable screen and the well bore. Even in circumstances in which it is practical to place a screen without a gravel pack, it is often difficult to determine an appropriate screen size to use as formation sands tend to have a wide distribution of sand grain sizes. When small quantities of sand are allowed to flow through a screen, screen erosion becomes a significant concern. As a result, the placement of gravel as well as the screen is often necessary to control the formation sands.
Another method used to control particulates in unconsolidated formations involves consolidating a subterranean producing zone into hard, permeable masses. Consolidation of a subterranean formation zone often involves applying a resin followed by a spacer fluid and then a hardener. Such resin application may be problematic or impractical for treating long intervals of unconsolidated regions due to the difficulty in determining whether the entire interval has been successfully treated with both the resin and the external catalyst. For long intervals, the placement of a consolidation resin along the formation is quite challenging due to the fact that most of aqueous resin will flow into the high permeability formation zone, resulting in the low permeability zone receiving less than the desired consolidation treatment.
Preventing formation sand and fines from migrating from an unconsolidated formation has always been a challenge.